Hitherto, in general, a coated tool in which the surface of a cutting tool body made of tungsten carbide (hereinafter, referred to as WC)-based cemented carbide, titanium carbonitride (hereinafter, referred to as TiCN)-based cermet, or cubic boron nitride (hereinafter, referred to as cBN)-based ultra-high pressure sintered material (hereinafter, collectively referred to as a cutting tool body) is coated with a Ti—Al-based complex nitride layer as a hard coating layer through a physical vapor deposition method, is known. It is known that such a coated tool exhibits excellent wear resistance.
Although the conventional coated tool coated with the Ti—Al-based complex nitride layer has relatively excellent wear resistance, in a case of using the coated tool under high-speed intermittent cutting conditions, abnormal wear such as chipping easily occurs. Therefore, various suggestions for an improvement in the hard coating layer have been made.
For example, PTL 1 discloses that a hard coating layer is formed on the surface of a cutting tool body. The hard coating layer is made of an Al and Ti complex nitride layer which satisfies a composition formula (AlxTi1-x)N, provided that x is 0.40 to 0.65 in terms of atomic ratio. In a case where crystal orientation analysis is performed on the complex nitride layer through electron backscatter diffraction (EBSD), the area ratio of crystal grains with a crystal orientation <100> in a range of 0° to 15° from a direction of the normal line to a polished surface is 50% or more, and in a case where angles between the crystal grains adjacent to each other are measured, a crystal arrangement in which the proportion of low-angle grain boundaries (0°<θ≤15°) is 50% or more is exhibited. PTL 1 discloses that by depositing the hard coating layer made of the Al and Ti complex nitride layer on the surface of the cutting tool body, the hard coating layer exhibits excellent defect resistance even under high-speed intermittent cutting conditions.
In the coated tool of PTL 1, since the hard coating layer is deposited by a physical vapor deposition method, it is difficult to cause the content ratio x of Al to be 0.65 or more, and a further improvement in cutting performance is desired.
From this viewpoint, a technique for increasing the content ratio x of Al to about 0.9 by forming a hard coating layer through a chemical vapor deposition method is suggested.
For example, PTL 2 describes that by performing chemical vapor deposition in a mixed reaction gas of TiCl4, AlCl3, and NH3 in a temperature range of 650° C. to 900° C., a (Ti1-xAlx)N layer in which the content ratio x of Al is 0.65 to 0.95 can be deposited. However, PTL 2 is aimed at further coating the (Ti1-xAlx)N layer with an Al2O3 layer and thus improving the heat insulation effect. Therefore, the effect of the formation of the (Ti1-xAlx)N layer in which the content ratio x of Al is increased to 0.65 to 0.95 on cutting performance is not clear.
In addition, for example, PTL 3 suggests that the heat resistance and fatigue strength of a coated tool are improved by coating the outside of a TiCN layer and an Al2O3 layer as inner layers with a (Ti1-xAlx)N layer with a cubic structure or a cubic structure including a hexagonal structure as an outer layer using a chemical vapor deposition method, provided that x is 0.65 to 0.90 in terms of atomic ratio, and applying a compressive stress of 100 to 1100 MPa to the outer layer.